Drying The Sky

Visitor Publish by Willis Eschenbach

Eleven years in the past I printed a submit right here on Watts Up With That entitled “The Thermostat Speculation“. A few 12 months after the submit, the journal Power and Setting printed my rewrite of the submit entitled “THE THUNDERSTORM THERMOSTAT HYPOTHESIS: HOW CLOUDS AND THUNDERSTORMS CONTROL THE EARTH’S TEMPERATURE“.

After I began finding out the local weather, what I discovered shocking was not the warming. For me, the oddity was how steady the temperature of the earth has been. The system is dominated by nothing extra substantial than wind, wave, and cloud. All of those are altering on each lengthy and brief time cycles the entire time. As well as, the floor temperature is working some thirty levels C or extra hotter than can be anticipated given the energy of the solar.

Regardless of that, the earth’s temperature has stayed in a surprisingly slender vary, e.g. ± zero.three°C over the complete 20th Century. This represents a temperature variation of ±zero.1% throughout 100 years. That stability was the curiosity of curiosities for me, as a result of to me that temperature stability was clear proof of some sort of a powerful thermoregulatory system. However the place and what was the regulating mechanism?

The brief model of my speculation is that a wide range of emergent phenomena function in an overlapping style to maintain the earth’s temperature steady past expectations. These phenomena embrace tropical cumulus clouds, thunderstorms, mud devils, squall strains, tornadoes, the La Nina pump shifting heat water to the Poles, tropical cyclones, and the Julian-Madden, Pacific Decadal and North Atlantic Oscillations. As well as, I’ve adduced a big physique of proof supporting my speculation.

So I used to be to see Judith Curry, in her marvelous weekly submit entitled “Week in evaluate – science version“, had linked to a paper I’d by no means seen. It’s a paper from 2010 by Marat F. Khairoutdinov and Kerry A. Emanuel (hereinafter Ok&E) entitled AGGREGATED CONVECTION AND THE REGULATION OF TROPICAL CLIMATE, accessible right here. Inter alia they are saying:

Moist convection within the Earth’s environment is usually composed of comparatively small convective clouds which are sometimes a couple of kilometers in horizontal dimension (Byers and Braham, 1948, Malkus, 1954). These typically merge into larger clusters of ~10 km in horizontal dimension, resembling air-mass showers. Extra not often, below particular circumstances, moist convection is organized on even bigger scales; this consists of squall strains (e.g. Houze, 1977), mesoscale convective complexes, (e.g. Maddox, 1980), and tropical cyclones.

One of many strong traits of self-aggregation is the somewhat dramatic change within the imply state that accompanies it. Particularly, in all non-rotating experiments (Bretherton et al., 2005) and an experiment on an f-plane (Nolan et al., 2007), self-aggregation results in dramatic drying of the domain-averaged surroundings above the boundary layer. This seems to be the results of extra environment friendly precipitation inside the convective clump as extra of the condensed water falls out as rain and fewer is detrained to the surroundings, per unit updraft mass flux. Such dramatic drying would scale back the greenhouse impact related to the water vapor, and thus, would result in cooling of the SST, which in flip might disaggregate convection. This may re-moisten the environment, rising the water-vapor greenhouse impact, and, consequently, warming the system. So, as in self-organized criticality (SOC), the tropical state can be interested in the transition important state between the aggregated and disaggregated states.

Let me level out a couple of issues about their most attention-grabbing research. First, they’re clear sturdy impact of the aggregated thunderstorms is to manage the tropical temperature … simply as I’ve been saying for years.

Sadly, their research is model-based. That is all the time irritating to me as a result of there isn’t a approach to test both the standard of their fashions or what number of runs ended up on the slicing room flooring …

Nevertheless, on condition that shortcoming, their research factors to one thing I famous in my authentic submit—not simply aggregated thunderstorms but in addition particular person thunderstorms dry out the air in between them. This has two large cooling results on the floor. 

First, the dry descending air permits for elevated evaporation from the floor, as a result of the dry air can choose up extra moisture from the floor. This elevated evaporation cools the floor.

Along with the elevated evaporation, the impact they mentioned is that the dryer air descending across the thunderstorms reduces the quantity of the world’s most important greenhouse gasoline, water vapor, that’s between the floor and outer area. This enables the floor to radiate extra freely to area, which additionally tends to chill the floor.

Of their abstract they are saying:

Idealized simulations of radiative-convective equilibrium counsel that the tropical environment might have not less than two steady equilibrium states or phases, one is convection that’s random in time and area, and the second is the spontaneously aggregated convection. On this research, we now have demonstrated utilizing a simplified and full-physics cloud-system-resolving fashions that there’s an abrupt section transition between these two equilibrium states relying on the floor temperature, with larger SST being conducive to the aggregation. A major drying of the free troposphere and consequent discount of the greenhouse impact accompany self-aggregation; thus, the sea-surface temperature within the aggregated state tends to fall till convection is pressured to disaggregate.

So, large credit score to them for noticing the thermostatic impact within the tropics. Nevertheless, their look is tightly targeted. They’ve appeared solely at one cooling mechanism. As well as, they’ve solely checked out two of what are not less than 4 of what they name steady equilibrium states or phases. Nevertheless, once more to their credit score they’ve mentioned “not less than” two steady states, acknowledging the existence of others.

Since Khairoutdinov and Emanuel had demonstrated utilizing fashions that dry air elevated with rising aggregated thunderstorms, I assumed I’d check out, you understand … observations. Information. Loopy, I do know, since a lot consideration is paid to fashions, however I’ve been a pc programmer far too lengthy to place a lot religion in fashions.


Let me begin by saying that they’re wanting on the third and fourth steady equilibrium states in the complete spectrum of the every day tropical thermally-driven threshold-based atmospheric response to rising floor temperature. Every of those steps entails self-organized criticality. 

Within the tropics, by daybreak, significantly over the ocean, the night-time environment is usually steady and thermally stratified, with clear skies at daybreak.

Step one is when the photo voltaic warming of the floor warms the air above it sufficient to provoke the steady equilibrium state referred to as Rayleigh-Benard convection. As is widespread with such self-organized transitions, as soon as the important transition temperature is exceeded, the change between states is speedy. 

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As soon as Rayleigh-Benard circulation is established, areas of ascending air are interspersed with areas of descending air. The areas of rising air, typically referred to as “thermals”, switch floor warmth and floor water vapor upwards. This cools the floor straight via conduction, as a result of the air touring throughout the floor picks up warmth from the floor. The R-B circulation additionally will increase thermal radiation to area from the upward motion of the nice and cozy air above the bottom environment, which comprises the best quantity of greenhouse gases. 

Lastly, the R-B circulation will increase evaporation by shifting the floor moisture upwards and mixing a few of it into the bottom a part of the troposphere.  This transition to R-B circulation is usually invisible, though the onset of every day overturning can typically be felt within the wind.

The second transition is once more temperature-based. It happens when the floor temperature is giant sufficient to drive the Rayleigh-Benard circulation larger into the troposphere. Within the tropics, this transition sometimes occurs within the late morning. When the water vapor within the ascending columns of the Rayleigh-Bernard circulation is moved upwards to the “LCL”, the “lifting condensation degree” the place water vapor condenses, at that altitude cumulus clouds type. The water vapor within the air condenses into the acquainted puffy cotton-ball cumulus clouds. Every particular person cumulus cloud group sits like a flag marking an ascending a part of the Rayleigh-Benard circulation proven above. 

Once more, the transition is speedy. Within the area of a few half-hour, the complete tropical atmospheric horizon to horizon can go from clear air to a completely developed cumulus area. And once more, the transition is temperature-based. Beneath a sure temperature, there are hardly any cumulus clouds in any respect. Above that temperature, all of a sudden there are many cumulus clouds.

The third transition happens when a considerably larger temperature threshold is exceeded. The third stage of growth is when particular person cumulus clouds self-aggregate into scattered cumulonimbus. They construct tall cloud towers, and the rain begins.

After this transition to the thunderstorm state, giant areas of descending dry air type round every thunderstorm. That is the return path of the air that was first stripped of water within the base of the thunderstorm. When the water vapor condenses it provides up warmth. The heated air then strikes up the thunderstorm tower, emerges on the prime, and descends as dry air within the areas across the thunderstorm. 

This stage, of lively thunderstorms, is effectively illustrated in probably the most entrancing simulation proven beneath. The coloured layer added at one minute twenty seconds exhibits the temperature of that layer, with darkish blue being coldest and purple/orange being warmest.

The fourth and ultimate transition happens solely in sure situations on the highest transition temperature, when particular person thunderstorms self-aggregate into squall strains and supercells, medium-scale convective complexes, and tropical cyclones. That is the one one of many 4 steady equilibrium states studied by Khairoutdinov and Emanuel. As with the opposite transitions, they level out that it’s related to a transition temperature. Just like the thunderstorm regime, areas of descending dry air type across the aggregated phenomena. Right here’s a photograph of a single squall line from area.

It’s value noting that every of those succeeding phases displays a rise within the charge at which the floor loses warmth. With every transition, the speed of floor warmth loss will increase from a wide range of causes. The trigger that’s mentioned by Ok&E, elevated radiation to area via drier air, is just one amongst many.

The primary transition, from quiescent stratified night-time environment to Rayleigh-Benard circulation, will increase floor warmth loss to the environment via conduction and convection of each latent and smart warmth. It encourages atmospheric loss to area by shifting the floor warmth up above the bottom atmospheric ranges with their denser focus of the greenhouse gases, principally water vapor and CO2. It mixes floor warmth and floor water vapor upwards. As a result of water vapor is lighter than air, the ascending areas are moister and the descending areas are dryer within the R-B circulation.

The second transition, to the cumulus area, provides two new strategies of cooling the floor. First, vitality is moved from the floor aloft within the type of latent warmth. This warmth is launched when the rising columns of air condense into clouds. The solar then re-evaporates the water from the higher floor of the clouds, and the water vapor mixes upwards. This strikes the floor warmth effectively up into the decrease troposphere.

The cumulus area additionally cools the floor by reflecting daylight again to area. This can be a very giant change within the vitality steadiness, on the order of a few hundred watts per sq. metre or so. The timing and density of the emergence of the cumulus area is among the main thermal regulation mechanisms. How sturdy is that this regulatory motion? Right here’s a typical day’s accessible photo voltaic vitality, measured at ten-minute intervals at a TAO buoy within the Equatorial Pacific Ocean.

The deep notch within the accessible photo voltaic vitality from clouds masking the solar at round 11:30 AM within the graphic above is kind of typical of the drop when clouds cowl the solar. On at the present time it lasted about half an hour. It decreased the accessible photo voltaic vitality flux by about six watts per sq. metre averaged over that 24 hour interval.

By comparability, a theoretical doubling of CO2 from the current, which is very unlikely to occur, would add a flux of about three.7 watts per sq. metre throughout that 24 hour interval.

So in that space, that one cloud can be greater than sufficient to cancel out even a doubling of CO2 for that day … and that’s simply one of many some ways the floor is being cooled by emergent phenomena.

The third transition, from developed cumulus area to scattered thunderstorms, provides the entire vary of recent floor cooling strategies that I checklist within the endnotes. And in contrast to the primary two transitions, thunderstorms can really cool the floor to a temperature beneath the temperature wanted to provoke the thunderstorms. This enables thunderstorms to take care of floor temperatures. When any location will get scorching a thunderstorm varieties and cools the floor again down, not simply to the place it began, however down beneath the onset temperature. This “overshoot” is the signature of a governor versus a easy linear or comparable suggestions. Easy suggestions can solely cut back a warming tendency. A governor, alternatively, can flip warming into cooling.

Within the fourth transition, the transition to the bigger self-aggregated phenomena like squall strains, supercells, and the like, no new floor cooling strategies are added. What occurs as a substitute is that the earlier strategies transfer to a brand new degree of effectivity. For instance, thunderstorms self-organize into squall strains as proven within the picture above. 

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As a substitute of particular person areas of descending air round every particular person thunderstorm, in a thermally-driven squall line you get lengthy rolls of dry descending air alongside the flanks of the squall line. As a result of the carpet-roll-type circulation is streamlined, with the air easily rolling in a protracted tube, the squall line strikes extra vitality from the floor to the higher troposphere than can be moved by the identical variety of particular person thunderstorms.

To summarize the dialogue to this point:

There are 4 distinct successive emergent transitions from a quiescent stratified environment to completely developed squall strains. Every is the results of self-organized criticality. Each is a separate emergent phenomenon, coming into existence, persisting for some longer or shorter time, after which disappearing. So as, the transitions and the brand new emergent phenomena are:

Nonetheless air to Rayleigh-Benard circulationRayleigh-Benard circulation to cumulus area.Cumulus area to scattered thunderstormsScattered thunderstorms to aggregated thunderstorms.

Every transition removes extra vitality from the floor to the environment and thus finally from the system.

Khairoutdinov and Emanuel focus on drying of descending air in solely one of many states, the fourth one the place thunderstorms combination. They’re right. Nevertheless, this doesn’t start on the fourth stage. All of the phases dry the descending air. And after every succeeding transition, the air turns into dryer and dryer.

I’ve demonstrated the shut dependence of thunderstorms and “aggregated” thunderstorms on the floor temperature. I made up a film displaying this some time again utilizing the CERES information, dangle on … OK, right here it’s. I’m utilizing the extent of deep convection as measured by the cloud prime heights as a measure of the energy of the thunderstorms and aggregates.

Within the film, you possibly can see the thunderstorms and aggregated thunderstorms (shade) following the nice and cozy water (grey strains) across the Pacific all year long. 

And if we take a scatterplot of common cloud prime altitude versus sea floor temperature, we discover the next relationship: 

Simply as we noticed within the film above, when the ocean floor temperature goes over about 26°C thunderstorms explode vertically, getting taller and taller. That is clear assist for the concept the transition between states is temperature-threshold primarily based.

With all of that as prologue, let me transfer to the query of the descending dry air between the thunderstorms. I noticed that we even have some superb details about the quantity of water within the air. That is information from the string of what are referred to as the TAO/TRITON buoys and different moored buoys that stretch on either side of the Equator all over the world. Listed here are their places.

Let me start with one other take a look at rainfall and temperature. Right here’s a scatterplot of the ocean floor temperature versus the rainfall within the equatorial Pacific space proven by the yellow field above (130°E – 90°W, 10°N/S). The blue dots beneath present outcomes from the TAO buoys within the yellow field. The purple dots present gridcell outcomes from the Tropical Rainfall Measuring Mission (TRMM) satellite tv for pc rainfall information and Reynolds OI sea floor temperatures.

Man, I do adore it when a number of completely unbiased datasets agree so effectively. Within the graph above the blue dots are co-located measurements of common rainfall and sea floor temperature at particular person TAO/Triton buoys. The purple dots are 1° latitude by 1° longitude averages of Reynolds OI Sea Floor Temperatures, and Tropical Rainfall Measuring Mission (TRMM) satellite-based rainfall information. And in each datasets, we see as soon as once more that thunderstorms begin forming in numbers solely when sea floor temperatures get above about 26°C.

It’s additionally attention-grabbing that when the ocean floor temperature will get into the upper-temperature vary, there are not any dry areas. Each place will get not less than a sure minimal quantity of rain. Not solely that, however the minimal quantity of annual rainfall will increase easily and exponentially as the typical sea floor temperature goes up.

Why is it so necessary that this threshold is temperature primarily based? It’s necessary for what it’s NOT. It isn’t forcing primarily based. In different phrases, the good international thunderstorm-based air-conditioning and refrigeration system kicks in at about 26°C, it doesn’t matter what the forcing is doing. It doesn’t matter what the CO2 is doing. It doesn’t matter what the volcanoes are doing. The regime shift from puffy white cumulus clouds to scattered thunderstorm towers kicks in when the temperature passes a temperature threshold, and never earlier than, no matter what CO2 does.

And this, in flip, signifies that these successive regime shifts, first to Rayleigh-Benard circulation, then to the cumulus area, then to scattered thunderstorms, and at last to aggregated thunderstorms, are functioning in a bunch of various methods to manage and cap the floor temperature.

And at last, by a reasonably circuitous however attention-grabbing route, we’ve arrived again on the query of the drying of the air in between the thunderstorms and thunderstorm aggregations.

There are eight TAO buoys which are straight on the Equator throughout the Pacific. It’s an attention-grabbing group as a result of all of them get an identical sunshine. Regardless of getting an identical photo voltaic vitality, there’s a temperature gradient from Central America throughout to Asia, with the Asian finish at about 29°C and the South American finish at about 24°C. So these eight buoys provides us a take a look at how some phenomena range by temperature. 

Utilizing the temperature and the relative humidity measurements from these buoys, I calculated absolutely the humidity for every of them. That is the quantity of water that’s current per cubic metre of air. That quantity is necessary as a result of the absorption of long-wave radiation by water vapor varies proportionally to absolutely the humidity, not the relative humidity. Much less absolute humidity means extra floor warmth loss by long-wave radiation to area.

These observations from the buoys are performed each ten minutes. This enables me to calculate what a median day’s variations appear to be. To grasp the every day variations, I aligned them on the morning minimums. Listed here are the information of these eight TAO buoys which are straight on the Equator.

On this graph, be aware that the hotter that the ocean floor temperatures are, the smaller the 10 AM peak, and the extra the afternoon absolute humidity drops from the 10 AM peak.

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It is because because the thunderstorms type and enhance the native space moisture is concentrated within the small space in and below the thunderstorms, with descending dry air between the thunderstorms making up the majority of the decrease troposphere. And in areas with hotter sea floor temperatures, proven in purple above, clouds and thunderstorms type earlier, are denser, and at occasions type even bigger aggregations of thunderstorms.

Now, what I’ve proven above are long run full-dataset averages. So it’s tempting to assume “effectively, thunderstorms solely occur the place the typical temperature is over 26°C”. However thunderstorms will not be touched by averages. These temperature-regulating phenomena can seem, persist, and disappear at any time of day. All that issues are the instantaneous situations. Each time the tropical ocean will get heat sufficient, whatever the longer-term averages for that location, you’re more likely to see thunderstorms type. All of the averages imply is that the floor will get sufficiently scorching to create thunderstorms on extra or fewer days of the 12 months.

My conclusions?

Ok&E have been proper concerning the drying energy of aggregated thunderstorms. 

It’s also true that particular person thunderstorms, in addition to cumulus clouds and Rayleigh-Benard circulation, dry out the descending air.

This decrease degree of water vapor cools the floor by rising radiation loss to area and by rising evaporation.

That is solely one of many host of ways in which cumulus clouds and thunderstorms maintain the tropics from overheating

Rayleigh-Benard circulation, cumulus fields, scattered thunderstorms, and aggregated thunderstorms are all emergent phenomena. They emerge wherever there’s adequate floor warmth, which means when the temperature exceeds some native threshold. Every succeeding state, in flip, begins eradicating extra warmth from the floor. That is an especially environment friendly temperature regulating system as a result of they emerge solely as and the place there are native concentrations of floor warmth.

Lastly, I need to emphasize considered one of Ok&E’s attention-grabbing claims:

Such dramatic drying would scale back the greenhouse impact related to the water vapor, and thus, would result in cooling of the SST, which in flip might disaggregate convection. This may re-moisten the environment, rising the water-vapor greenhouse impact, and, consequently, warming the system. So, as in self-organized criticality (SOC), the tropical state can be interested in the transition important state between the aggregated and disaggregated states.

In different phrases, all of those phenomena act to stabilize the temperature.

Right here, sunshine. Life is nice. My perfect needs to all.


My Regular Request: If you remark please quote the precise phrases that you’re referring to, so we will all perceive your topic.


Ok&E are wanting simply at elevated radiation via dryer air. That is solely one of many many ways in which thunderstorms cool the floor. Right here’s a extra full checklist.

• Refrigeration-cycle cooling. A house fridge evaporates a working fluid in a single location and condenses it in one other location. This removes warmth within the type of latent warmth of evaporation/condensation. The thunderstorm makes use of the very same cycle. For the thunderstorm the working fluid is water. Water evaporates on the floor and is carried aloft through the thunderstorm circulation. This, in fact, removes floor warmth within the type of latent warmth. Then, simply as in a home refrigeration cycle, the working fluid condenses at altitude within the thunderstorm base and falls again as a chilly liquid to the floor.

• Self-generated evaporative cooling. As soon as the thunderstorm begins, it creates its personal wind across the base. This self-generated wind will increase evaporation in a number of methods, significantly over the ocean.

a) Evaporation rises linearly with wind velocity. At a typical squall wind velocity of 10 mps (20 knots), evaporation is about ten occasions larger than at “calm” situations (conventionally taken as 1 mps).b) The wind will increase evaporation by creating spray and foam, and by blowing water off of timber and leaves. These significantly enhance the evaporative floor space, as a result of the full floor space of the hundreds of thousands of droplets is evaporating in addition to the precise floor itself.c) To a lesser extent, floor space can also be elevated by wind-created waves (a wavy floor has a bigger evaporative space than a flat floor).d) Wind created waves in flip significantly enhance turbulence within the atmospheric boundary layer. This will increase evaporation by mixing dry air right down to the floor and moist air upwards.

• Wind-driven albedo enhance. The white spray, foam, spindrift, altering angles of incidence, and white breaking wave tops significantly enhance the albedo of the ocean floor. This reduces the vitality absorbed by the ocean.

• Chilly rain and chilly wind. Because the moist air rises contained in the thunderstorm’s warmth pipe, water condenses and falls. Because the water is originating from condensing or freezing temperatures aloft, it cools the decrease environment it falls via, and it cools the floor when it hits. As well as, the falling rain entrains a chilly wind. This chilly wind blows radially outwards from the middle of the falling rain, cooling the encompassing space.

• Elevated reflective space. White fluffy cumulus clouds will not be tall, so mainly they solely mirror from the tops. However, the vertical pipe of the thunderstorm displays daylight alongside its total size. Which means thunderstorms shade an space of the ocean out of proportion to their footprint, significantly within the late afternoon.

• Modification of higher tropospheric ice crystal cloud quantities (Lindzen 2001, Spencer 2007). These clouds type from the tiny ice particles that come out of the smokestack of the thunderstorm warmth engines. It seems that the regulation of those clouds has a big impact, as they’re thought to heat (via IR absorption) greater than they cool (via reflection).

• Enhanced night-time radiation. Not like long-lived stratus clouds, cumulus and cumulonimbus typically die out and vanish because the evening cools, resulting in the sometimes clear skies at daybreak. This enables significantly elevated nighttime floor radiative cooling to area.

• Supply of dry air to the floor. The air being sucked from the floor and lifted to altitude is counterbalanced by a descending circulate of alternative air emitted from the highest of the thunderstorm. This descending air has had the vast majority of the water vapor stripped out of it contained in the thunderstorm, so it’s comparatively dry. The dryer the air, the extra moisture it may well choose up for the following journey to the sky. This will increase the evaporative cooling of the floor in addition to permitting extra radiative loss to area.

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